Black-and-white images formed in a photographic process are generally produced by developing silver halide in a black-and-white developer to form a silver image. A black-and-white developer, such as hydroquinone, is commonly used to reduce the exposed silver halide to silver metal. The undeveloped silver halide is removed from the print by `fixing` with aqueous sodium thiosulfate. The silver metal remaining in the print represents the image.
In the photographic industry, a photofinisher who wishes to produce both black-and-white and color pictures or prints must have separate processing systems; one for color and one for black-and-white, as the two systems are not compatible. It would, therefore, be advantageous for the photofinisher to have one process capable of producing either black-and-white or color materials.
U.S. Pat. No. 4,348,474--Scheerer discloses a system wherein black-and-white images are formed by the use of one emulsion that is treated with three sensitizing dyes.
U.S. Pat. No. 2,186,736--Schneider discloses the use of several color components in one layer for a black-and-white image formation.
U.S. Pat. No. 2,592,514--Harsh discloses a color film in which couplers forming more than one color are present in the same layer of the color film.
There have been commercialized products that have formed black-and-white images by the use of pan sensitized emulsions which contain three spectral sensitizing dyes, color dye forming couplers and one emulsion. These pan-sensitive emulsions are sometimes coated in a fast and a slow layer to form images after exposure and development of the couplers. While the above products are somewhat successful, they do not achieve a neutral image. Additionally, the tone reproduction of such materials is severely limited by the contrast range of the emulsion.